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Could Apoquel medication be the cause of my dog's mast cell tumor?

Updated On September 23rd, 2025

Pet's info: Dog | American Pit Bull Terrier | Male | neutered | 60 lbs

My daughter has a 5 year old pit bull/lab mix who was just diagnosed with a mast cell tumor on his hind leg. He was started on Apoquel in the past 90 days. She is a pharmacist and naturally read the insert on possible side effects, one of which was this tumor. She is very upset and blaming herself, understandably. What is your experience on the number of dogs that develop this tumor after taking this med? She is waiting for the biopsy results for the grade/stage.

3 Answers

Most Helpful Answer

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Answered By Megan, DVM, CVA

Veterinarian

Published on August 9th, 2017

I have NEVER seen this. I read the package inset and the study shows that 1 dog out of 147 dogs in the PLACEBO group develop a mast cell tumor. Since he was in the placebo group he was actually not receiving the apoquel medication. And then in another study 2 dogs out of 239 dogs that were receiving apoquel develop a mast cell tumor. That is 0.8% that develop a mast cell tumor. Since the percentage is so low then the likelihood of the medicine causing the tumor is very unlikely. These dogs were likely going to develop mast cell tumor whether on the medicine or not. I hope this helps to settle your daughters mind and doesn't blame herself. I do not believe the medicine caused the tumor.

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Other Answers

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    Answered By Stephanie Echols, DVM

    Veterinarian

    Published on

    I'm sorry to hear about your daughters dog. As she knows, the listed side effects are anything finding that occurs while on the medication. This means that the pet on Apoquel could have developed a mast cell tumor while on the medication or he could have developed the tumor when not given Apoquel. In my experience I have not seen a dog develop a tumor from Apoquel. I think this is just a coincidence. Continue with the mass staging and tell her to have it removed. Commonly this is curative. I hope this helps! Kisses to the pup!

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    0Pet Parents found this answer helpful

  • Image profile

    Answered By Megan, DVM, CVA

    Veterinarian

    Published on

    I have NEVER seen this. I read the package inset and the study shows that 1 dog out of 147 dogs in the PLACEBO group develop a mast cell tumor. Since he was in the placebo group he was actually not receiving the apoquel medication. And then in another study 2 dogs out of 239 dogs that were receiving apoquel develop a mast cell tumor. That is 0.8% that develop a mast cell tumor. Since the percentage is so low then the likelihood of the medicine causing the tumor is very unlikely. These dogs were likely going to develop mast cell tumor whether on the medicine or not. I hope this helps to settle your daughters mind and doesn't blame herself. I do not believe the medicine caused the tumor.

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    1Pet Parents found this answer helpful

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